Chapter 12 BIG IDEAS Newtons laws apply to all forces Gravity is a force exerted by all masses Friction is a force that opposes motion Pressure depends on force and area Fluids exert a force on objects ID: 539459
Download Presentation The PPT/PDF document "Forces and Fluids" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Forces and Fluids
Chapter 12Slide2
BIG IDEAS
Newton’s laws apply to all forces
Gravity is a force exerted by all masses
Friction is a force that opposes motion
Pressure depends on force and area
Fluids exert a force on objectsSlide3
PressureSlide4
What is Pressure?
Related to the word press
Earth’s gravity pulls downward
Due to gravity, your feet exert a force on the surface of Earth over an area the size of your feetSlide5
Pressure and Area
The amount of pressure you exert depends on the area over which you exert force.
Larger area = less pressure exertedSlide6
Calculating Pressure
Pressure =
Force
Area
Measured in
Pascals
– 1 N/m²Slide7
Fluid Pressure
Fluid
is a material that can easily flow
Liquids
Gases
Air and helium
Viscosity – a liquid’s
r
esistance to flow
-the
s
lower the flow the
m
ore viscous
ex. Syrup is more
viscous than waterSlide8
What Causes Fluid Pressure
In a fluid, all of the forces exerted by the individual particles combine to make up the pressure exerted by the fluid.Slide9
Air Pressure
Air exerts pressure because it has mass
Because the force of gravity pulls down on the mass of air, the air has weight
Weight of the air is the force that produces air pressure or atmospheric pressureSlide10
Balanced Pressure
Hold out your hand
Holding up air – 1,000 N
About the same weight as that of a large washing machineSlide11
Unbalanced Pressure
What happens when air pressure becomes unbalanced?Slide12
Variations in Fluid Pressure
Atmospheric Pressure and Elevation
Popping in ear is caused by changing air pressure.
Higher elevations – less air above you = less air pressure
*Atmospheric pressure decreases as your elevation increasesSlide13
Variations in Fluid PressureSlide14
Variations in Fluid Pressure
Water Pressure and Depth
Water pressure increases as depth increases
Deepest part of the ocean 1,000 times greater air pressure than we experience every day
Volume of water does not effect amount of pressure only depthSlide15
Measuring Pressure
Barometer
measures atmospheric pressureSlide16
Floating and SinkingSlide17
Density
Comparing densities, you can predict whether an object will float or sink in a fluid.
If object is more dense than fluid – it sinks
If object is less dense than fluid
- it floats
An object with
a density
equal to that of the fluid floats at a constant depth.Slide18
Density
Density =
Mass
Volume
Density of water = 1.0Slide19
DensitySlide20
Changing Density
Changing density can explain why an object floats or sinks.
SubmarineSlide21Slide22Slide23
Buoyancy
Buoyancy
is the ability to float. Slide24
Buoyant Force
Buoyant force is when water and other fluids exert an upward force.
The buoyant force acts in the direction opposite to the force of gravity, so it makes an object feel lighter.
The less dense the object is, the greater the buoyant force it experiences.Slide25
Buoyant ForceSlide26
Buoyant ForceSlide27
Buoyant ForceSlide28
Archimedes’ Principle
The buoyant force acting on a submerged object is equal to the weight of the volume of fluid displaced by the object.Slide29
Pascal’s PrincipleSlide30
Transmitting Pressure in a Fluid
In the 1600s,
Blaise
Pascal developed a principle to explain how pressure is transmitted in a fluid
Fluid exerts pressure on
any surface it touches.Slide31
Pascal’s Principle
Pascal’s principle states that pressure increases by the same amount throughout an enclosed or confined fluid
When force is applied to a confined fluid, the change in pressure is transmitted equally to all parts of the fluid.Slide32
Pascal’s Principle at WorkSlide33
Pascal’s Principle at WorkSlide34
Hydraulics
and the use of liquid pressureSlide35
Hydraulic Systems
Hydraulic system uses liquids to transmit pressure and multiply force in a confined fluid.
A hydraulic system multiplies force by applying the force to a small surface area. The increase in pressure is then transmitted to another part of the confined fluid, which pushes on a larger surface area.
Because hydraulic systems use fluids to transmit pressure, hydraulic systems have few moving parts that can jam, break or wear down. Slide36
The important features of pressure in liquids
Liquids will transmit pressure throughout the liquid, regardless of the shape of the container
A force therefore can be applied wherever you want it
The force can be multiplied according the the area of the pistons used to push down on the waterSlide37
Examples of the use of hydraulics
Car brakes
Car jacks
Fork lift trucks
Lifts
bulldozers
Television camerasSlide38
Hydraulic LiftsSlide39
How car brakes use hydraulics
A small force on the brake pedal will act on a piston with a small area
The small piston pushes against the brake fluid
The pressure exerted is transmitted to all parts of the liquid
The pressure acts against four bigger pistons with larger areas
The large pistons will multiple the force and cause the brake pads to push against the wheels
As pressure is transmitted equally throughout the liquid, each brake works evenly tooSlide40
Hydraulic brake
The diagram shows a simple brake where a pedal will push down on the smaller master piston
The force pushing down will put the liquid under pressure
The pressure is transmitted through the liquid and against the slave piston
The pressure causes the slave piston to exert a force where it is neededSlide41
Using the formula
P=F/A
What is the pressure exerted on the liquid by the slave piston?
Answer:
Pressure = 10N / 5cm2
= 2 N/cm
2
Calculate the area of the slave piston that will lift a 100N load
Answer:
Area = force / pressure
= 100N / 2 N/cm
2
Master
Piston
Is 5 cm
2
10N
Slave pistonSlide42
More questions on hydraulics
What will the force (F1) need to be to exert a pressure of 20 N/cm2 ?
Calculate the weight (F2) that can be lifted by the slave piston.
Answers:
1. Force = 20 N/cm
2
x 10cm
2
= 200N
2. Force = 20 N/cm
2
x 100cm
3
= 2000N
Master piston = 10cm
2
Slave piston = 100cm
2Slide43
Hydraulic LiftsSlide44
Hydraulic BrakesSlide45
Hydraulic BrakesSlide46
Summary of the principles of hydraulics
Pressure is transmitted throughout a liquid
A force may be applied anywhere to the liquid
All hydraulic systems use a small master piston and a large slave piston
A small force is used to create a very big force
The small master piston is used to apply a force
The slave piston is always bigger than the master piston
The larger slave piston will multiply the original force put on the master piston